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Tail command limitations?

James Daniel
Ranch Hand

Joined: Sep 24, 2004
Posts: 80
Does the "tail -f output.log" command in Unix always capture all output or does it pare it down if too much data is being outputted? Example: If I start tail -f command, and 10 seconds later an external program outputs 1000 lines of log file in period of 1 second or less, will the output contain all 1000 lines - or will it be truncated in some way? The reason why we want tail to be 100% accurate is because we plan on using the output of tail in a java program to process the logs automatically and we don�t want to lose any information. I was under the assuption that tail always captured all output no matter the rate of output. Is this incorrect?

[ April 23, 2007: Message edited by: James Daniel ]
[ April 23, 2007: Message edited by: James Daniel ]
Ernest Friedman-Hill
author and iconoclast

Joined: Jul 08, 2003
Posts: 24187

Is is not incorrect -- i.e., tail won't drop any data.

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James Daniel
Ranch Hand

Joined: Sep 24, 2004
Posts: 80
Ernest Friedman-Hill,

Thanks for the prompt reply. That is what we thought. A developer in our group was telling us this and we needed to verify. Thanks again..
Tim Holloway
Saloon Keeper

Joined: Jun 25, 2001
Posts: 16142

Tail does a seek to the end of the file, which is a basic function in Unix. So it's actually quite fast.

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It is sorta covered in the JavaRanch Style Guide.
subject: Tail command limitations?